A glass panel is often used as a front cover for an electronic device, for example a cellular telephone or smart phone. Electronic device manufacturers now desire back covers of electronic devices that are also made of glass and that meet the same high dimensional accuracy and surface quality as the front covers. Although it is possible to make the front and back covers separately with the requisite dimensional accuracy and surface quality and then assemble each with a case, this adds extra steps to the manufacturing process and can result in loss of dimensional control.
Methods for forming glass tubing from molten glass are known. The most common ones are the Danner process, the Vello process, and the downdraw process. These processes are described in, for example, Heinz G. Pfaender, “Schott Guide to Glass,” 2nd ed., Chapman & Hall, 1996. These processes are typically used to form glass tubing with a round cross-sectional shape. Extrusion can be used to form glass tubing with a non-round cross-sectional shape, e.g., a cross-sectional shape that could have flat sides. However, extrusion involves tool contact with the glass surface, which could diminish the surface quality of the glass. Non-round extrusions are harder to polish or otherwise post-treat to remove imperfections than are round extrusions, so the imperfections introduced by extrusion persist in the finished product. Current approaches have been limited by the quality of the products or by extremely low manufacturing speeds.